Add BLAS i?amax function

The old one, `idamax`, wasn't using BLAS's functions when possible.
Besides, it was the wrong name! According to the specification, the
correct name is ixamax (where x \in {f,d,c,z}).
Using imax instead of idamax
Return a Ruby Fixnum

This commit also removes some compilation warnings. (yay)
Add test for NMatrix::BLAS.cblas_imax
Add documentation to NMatrix::BLAS.cblas_imax
Merge pull request #231 from agarie/blas_imax_imin

Make NMatrix::BLAS.cblas_imax call BLAS functions
Remove extra whitespace
NMatrix::BLAS.cblas_scal make use of CBLAS

First of all, `xscal` (x in {s,d,c,z}) seems to be a BLAS level 1
function instead of a LAPACK one according to the standard[1]. Thus I
reworded it to reflect reality and added calls to the cblas routines
(which also solves an old FIXME).

I still don't know how everything works in the NMatrix C/C++ world, but
it appears to work correctly.

[1]: http://www.compsci.wm.edu/sciclone/documentation/software/math/ATLAS/blas-report.pdf
Add specs to NMatrix::BLAS.cblas_scal
Fix indentation
Add documentation for NMatrix::BLAS.cblas_scal
[BLAS scal] Fix compilation problem

I introduced a small problem by *not reading* variable names and blindly
copying BLAS interfaces. Anyway, this patch should make compilation
(and, obviously, specs) work correctly.